I mostly use heavy conicals and low powder charges. I feel the loss in velocity is made up by the greater mass of the bullet. When I shoot a muzzleloader I am not trying to mimic a centerfire rifle. If that was what I wanted, I would shoot a centerfire.
Anyway, it is foot pounds of energy when the projectile hits the deer that matters. Heavy conicals and 70 to 80 grains of powder will do the job nicely.
Art